Soft tissue injuries with the use of safe corridors for transfixion wire placement during external fixation of distal tibia fractures: an anatomic study

OBJECTIVES

To determine which soft tissue structures are at risk and when joint violation can occur during small wire placement for hybrid external fixation of distal tibial fractures while adhering to published guidelines.

DESIGN

Cadaver anatomic experiment.

SETTING

University orthopaedic program. SUJBECTS: Five embalmed cadavers.

INTERVENTION

Placement of small wire transfixion pins in the distal tibia.

MAIN OUTCOME MEASUREMENTS

Dissection and measurements.

METHODS

Four orthopaedic surgeons were shown diagrams that have been widely accepted as allowing for placement of transfixion pins in the distal tibia through safe corridors. Each of the orthopaedic surgeons was then asked to place two transfixion pins into each of five cadaver legs in a position that would provide stable external fixation of the metaphysis to the diaphysis with a circular fixator (forty pins total) for a distal tibial fracture within five centimeters of the plafond. The specimens were dissected, and pins impaling neurovascular structures, tendons, or the ankle capsule were recorded. The superior capsular synovial reflections were measured from the anterior joint line and the tip of the medial malleolus. These measurements were also performed on arthrograms of two extremities before their dissection.

RESULTS

Fifty-five percent of the pins placed impaled at least one tendon that crosses the ankle joint. Neurovascular structures that were impaled included the saphenous vein (+/-10.5 percent) and the superficial peroneal nerve (+/-7.5 percent). One pin violated the superior capsular synovial reflection, which was an average of thirty-two millimeters (+/-1.58 millimeters) from the tip of the medial malleolus and twenty-one millimeters (+/-1.63 millimeters) from the anteromedial joint line.

CONCLUSIONS

This study shows that tendons and neurovascular structures above the ankle are at risk during small transfixion pin placement, even when using safe corridors. Pins placed within two centimeters of the anterior joint line or three centimeters from the medial malleolus may be intracapsular.

Effect of distal fibular resection on ankle laxity

Ten cadaver specimens were used to study the effect of distal fibular resection and ligamentous repair on ankle laxity. The distal fibula was resected sequentially at three levels. Talar tilt and anterior drawer were measured on stress radiographs after resection and then after ligament repair. Sequential resection of the distal fibula caused a progressive increase in talar tilt and anterior drawer at each cut level (p < 0.5), regardless of whether the ligaments were repaired or not. Ligament repair significantly decreased talar tilt at cuts above the ATFL insertion and decreased anterior drawer at cuts at the tibiotalar level, but these values did not approach control values.